1. Field of Invention
The present invention relates to a global positioning system (GPS), and more particularly to a method for calculating current position coordinate and a method for calculating a pseudo range, which are applicable to a GPS receiver.
2. Related Art
Global navigation satellite system is also called GPS. In the past, the GPS is only limited to military purpose and industrial purpose. With the continuous development of the technology, the GPS begins to be applied to various civil purposes. Generally, the GPS products mainly refer to GPS receivers applied to various purposes, for example, receivers for aviation and voyage purposes, automobile navigation devices, hand-held receivers for mountaineering and entertainment, and other types of communication products. The common GPS product mainly includes an internal antenna, a chipset, external keys, a display panel, and other related parts.
The GPS receiver determines positions by utilizing satellites surrounding the earth.
When each satellite operates, one coordinate value representing the position (known) exists at any moment. The position coordinate of each satellite is provided by a respective ephemeris data of the satellite.
The position coordinate of the GPS receiver is unknown. The GPS receiver compares a clock of a satellite signal and a clock generated in the GPS receiver, so as to calculate the time cost during a process of transmitting the satellite signal. The time difference (that is, the time cost during the process of transmitting the satellite signal) value is multiplied by an electric wave transmission speed (generally the speed of light), so as to calculate a distance between the satellite and the GPS receiver, which is called a pseudo range. According to the triangle vector, a related equation is given for the pseudo range.
When the satellite signal of one satellite is received, one related equation is given. Therefore, when the satellite signals of three satellites are received, plane coordinate values (that is, longitude and latitude) are calculated. The calculated plane coordinate values are the position coordinate of the GPS receiver. When the satellite signals of four satellites are received, in addition to the plane coordinate values (that is, the longitude and the latitude), a height value is also calculated. Further, if the satellite signals of more than five satellites are utilized, the accuracy of the calculated position coordinate is improved.
Generally, the GPS receiver automatically and continuously receives the satellite signals, and re-calculates virtual coordinate at each second, so as to calculate the position coordinate of the position on real time. That is to say, the position coordinate of the GPS receiver at each second is the latest.
However, by reason of the effect of the environment during the process of transmitting the satellite signal, practically noises exist in the satellite signal received by the GPS receiver, such that the calculated pseudo range generates errors, so as to affect the accuracy of the positioning information (that is, the position coordinate of the current position of the GPS receiver).
In the prior art, mainly the effect of the noises is reduced by utilizing a kalman filter, but the achieved effect is quite limited.